Volumetric recorder with resilient loading on expandable bag



Jan. 9, 1968 D. R. GARBE 3,36

VOLUMETRIC RECORDER WITH RESILIENT LOADING ON EXPANDABLE BAG Filed Dec.'7, 1965 v 5 Sheets-Sheet 1 Inventor DIET/"MR RuooLr Gnnaa B fazae W Attorne yb D. R. GARBE 3,363,260.

VOLUMETRIC RECORDER WITH RESILIENT LOADING ON EXPANDABLE BAG Jan. 9,1968 5 Shees-Shet 2 Filed Dec. 7, 1965 Inventor DIET/MA Av 001.; 04MB: B/MJ Y A Home y:

D. R. GARBE Jan. 9, 1968 v VOLUMETRIC RECORDER WITH RESILIENT LOADING onEXPANDABLE BAG Filed Dec. 7, 1965 5 Sheets-Sheet 5 Invenlor DIET/mmllbhcLF MRPE 1 A Home I United States Patent 3,363,260 VOLUMETRICRECORDER WITH RESILIENT LOADING 0N EXPANDABLE BAG Dietmar R'Garbe, MaidsMoreton House, Maids Moreton, Buckinghamshire, England Filed Dec. 7,1965, Ser. No. 512,114

Claims priority, application Great Britain, Dec. 11, 1964,

50,657/64 Claims. (Cl. 346-72) ABSTRACT OF THE DISCLOSURE The inventionis concerned with recording spirometers of the inflatable bag type ofwhich the apparatus shown in Shipley, US. Patent No. 2,999,495 is atypical prior example. With such spirometers the patient exhalesforcibly into an inflatable bag and the movement of the bag duringinflation is recorded against time upon a graph. The shape of the graphshows the pattern of forced exhalation and physicians can by suitableinspection and measurement detect and evaluate certain pulmonaryconditions.

Heretofore, the graph has been distorted owing to the inertia of thepart of the apparatus moved by the bag. It has been found by theapplicant that the principal, and only significant distorting occurs atthe beginning of an inflation when the inertia causes the part to lag inits movement and at the end of the inflation when the inertia causes thepart to overshoot the true maximum and also to tend to give too high areading as inflation slows before stopping. Applicant overcomes thedifliculty by providing a resilient loading which pulls on the part atthe beginning of inflation and opposes its motion at the end ofinflation. In a typical arrangement shown in the drawings, the bag 6drives a normally horizontal hinged part 3 and the resilient loading isprovided in the form of over-centre spring 26 which in the rest positionpreferably just fails to lift the part 3. Inflation of the bag causesthe spring arrangement to pass through its dead centre. Thereafter ittends to pull the member downwardly and thereby helps to slow the motionof the hinged part 3 as exhalation is be ing completed.

In the result a graph of much less distorted shape is obtained.

The present invention relates to recording spirometers and has as anobject the provision of a recording spir0meter in a new and improvedform.

In recent years it has come to be recognised that a record showing thevolume of breath exhaled against time on a forced exhalation can be auseful aid in the diagnosis of various conditions. For producing such arecord it is convenient to provide a recording spirometer whichcomprises a pivotally mounted member, a breath-receiving bag expandableon being inflated by the breath to move the member progressively aboutits pivot and a recording device operable to record the movement of themember as a function of time. Such a spirometer, however, gives a recordwhich tends to be distorted.

The present invention is based on the discovery that the distortion is aresult of the tendency of the inertia of the pivotally mounted member tocause it to move non-linearly with the flow of breath into the bag, andthat this tendency can substantially be eliminated by providing themember with a resilient loading. Indeed the tendency may be eliminatedto such an extent that it becomes feasible to adjust the spirometerunder static conditions, in which the bag is supplied with variousmeasured volumes of air, and thereby achieve an accuracy of plus orminus 1%.

In a preferred arrangement the resilient loading is a spring arranged tobias the member towards an intermediate position of its movement.Conveniently, the spring is a tension spring secured in over-centrerelationship with the member.

The spirometer is most conveniently provided in such a form that themember is pivoted about a horizontal axis and lies horizontally when thebag is deflated, being raised as the bag is inflated. On the first entryof breath into the bag, movement of the member is assisted by theresilient loading so that, in spite of its inertia, it moves readily topermit the bag to expand. As exhalation by the patient is beingcompleted, the rate of flow of breath into the bag diminishes and theresilient loading now acts to help the member to decelerate in response.Additionally, by loading the member, it compensates for the in crease ofmechanical advantage of the bag thereon as the member approaches thevertical and the track of the center of gravity of the member approachesthe horizontal.

In a preferred form of the spirometer, the member is connected with astylus carried in operable relationship with a chart carrier movable byan electric drive motor, having equal starting and running torques,across the direction of the movement of the stylus caused by the memberand the motor has an energising circuit which is energised by meansresponsive to movement of the member.

The following description of a preferred embodiment of the invention, inwhich description reference is made to the accompanying drawings, isgiven by way of illustration.

In the drawings:

FIGURE 1 is an end elevation of the embodiment,

FIGURE 2 is a plan of the embodiment, and

FIGURE 3 is a perspective view of the embodiment complete with aprotective casing.

In the embodiment shown in the drawings, a base plate 1 has mountedthereon brackets 2, to which a member .3, constituted by a plateupwardly flanged at its perimeter, is pivotally carried on stub-spindles5 by arms 4 which project from said member.

Between the member 3 and the base plate 1 is a bag 6 accordion pleatedat three sides and connected by its fourth side, which is in its sidenearest to the pivotal axis of the member 3, with a wide breath inletconduit 7 leading from a coupling 8 which is accessible from the frontof the protective casing 9 (FIGURE 3).

An arcuate arm 10, having its centre of curvature on the pivotal axis ofthe member 3 is secured to the side of the member 3 remote from thepivotal axis thereof. The outer end of the arm 10 which projects throughan aperture 11 of the casing, carries a stylus 12 for marking a standardchart 13, printed on pressure sensitive card, held by a chart carrier14.

The chart carrier, which is cylindrically curved about the pivotal axisof the member 3, is slidably carried at its upper edge upon a bearingrod 15 by self-oiling bearings 16.

To the underside of the lower edge of the chart carrier 14 is secured anylon rack 17 engaged by a nylon pinion 18 having an electric drivemotor 19. The bearing rod 15 and the rack 17 run parallel with thepivotal axis of the member 3. The motor 19, which is of a type havingequal starting and running torques, is provided with an energisingcircuit which includes a micro-switch 20 responsive to a pin 21 carriedby the member 3. The circuit also includes a control button 22 and pilotlights 23 and 24, the arrangement being such that the motor can only runwhilst button 22 is held pressed, pilot light 24 glows when theapparatus is connected to the supply mains for use, and pilot light 23glows only when the motor is energised by the micro-switch 20.

Between the bag 6 and the base plate 1 is positioned a platform 25. Thisplatform is of such height and dimensions that it lies just within theaccordion pleating to hold the opposite, i.e., the upper and lower,faces of the bag in contact when the bag is deflated and the member 3 ishorizontal; in this way the dead-space within the bag, and thereforewithin the apparatus, is reduced to aminimum.

At each side of the member 3 a tension spring 26 is tensioned between ananchorage 27 near the edge of the member remote from the pivotal axisthereof, and an anchorage 28 carried by the brackets 2 at a greaterheight than the stub-spindles 5. Accordingly, when the bag is deflatedand the member 3 is in its lowermost position, the tension in thesprings acts against the weight of the member 3, the tension in factbeing just insufficient in itself to cause the member 3 to rise. Oninflation of the bag the member 3 passes through a dead-centre position,which corresponds with a 145 elevation of the member, the spring acts tooppose the pivotal movement of the member.

If a patient blows into the machine via a flexible tube connected withthe coupling 8 whilst b'utton 22 is held pressed and pilot light 23 isglowing, the bag begins to inflate. The dead-space being very small, themember 3 begins to move almost immediately and the resulting movement ofpin 21 actuates the microswitch to start the motor so that the chart 13on the carrier 14, moves, parallel with the pivotal axis of the member3, under the stylus 12 to provide the time component of a time/ volumecurve which is traced upon the chart by the stylus. Because of theinitial pull of the springs 26, the first movement of the member 3, andtherefore the stylus 12 tends to be uninhibited by the inertia of themember 3 and the parts attached thereto. After passage through the deadcentre position, deceleration of the member 3 as the flow rate of thebreath decreases, is assisted by the tension of the springs and thecurve traced by the stylus corresponds closely, e.g., as closely as 1%with the ideal.

The apparatus may be calibrated under static conditions by supplying thebag with a series of measured volumes of air and after each one loadingthe bag to produce the required stylus position by attaching lengths ofwire 29 between the accordion pleats which are provided with pockets(not shown) to receive them.

By the present invention, a recording spirometer of considerable dynamicaccuracy is provided in a very simple form.

I claim:

1. A recording spirometer, which comprises a pivotally mounted member, anormally empty breath-receiving bag expandable on being inflated by thebreath to move the member progressively about its pivot, a recordingdevice connected to the pivotally mounted member to record the movementof the member as' a function of time and a resilient loading connectedto the pivotally mounted member in over-centre relationship for themember by which resilient loading the tendency of the inertia of themember to cause it to start too slowly and subsequently overshoot andthereby move non-linearly with the flow of breath into the bag issubstantially eliminated.

2. A recording spirometer according to claim 1 in which the member ispivoted about a horizontal axis and lies horizontally when the bag isdeflated, being raised as the bag is inflated.

3. A recording spirometer, which comprises a pivotally mounted member, anormally empty breath-receiving bag expandable on being inflated by thebreath to move the member about its pivot, a recording device connectedto the pivotally mounted member to record the movement of the member asa function of time, the member being pivotally mounted about ahorizontal axis, lying horizontally when the bag is deflated and beingraised when the bag is inflated, a resilient loading connected to thepivotally mounted member in over-centre relationship which acts upon themember in such a direction as to raise it from the horizontal but justinsufliciently to cause the member to rise in the absence of inflationof the bag and also acts upon the member'to oppose its motion andthereby prevent the. member overshooting as inflation ceases, saidresilientmeans thereby substantially eliminating the tendency of theinertia of the member to cause it to move non-linearly with the flow ofbreath into the bag.

4. A recording spirometer according to claim 3 in which the bag isaccordion pleated and has opposite faces which are held in contact bythe member when the bag is deflated.

5. A recording spirometer according to claim 3 in which the member isconnected with a stylus carried in operable relationship with a chartcarrier movable by an electric drive motor, having equal starting andrun ning torques, and the motor has an energising circuit which isenergised by means responsive to movement of the member.

References Cited UNITED STATES PATENTS 408,938 8/1889 Tata 346721,863,929 16/ 1932 McKesson 1282.07 2,228,983 1/1941 Bloomheart 1282.072,569,849 10/1951 Emerson 128-2.08 2,999,495 9/1961 Shipley 1282.083,086,515 4/1963 Jones 1282.08

RICHARD B. WILKINSON, Primary Examiner.

J. W. HARTARY, Assistant Examiner.

